Process of making bifocal lenses



H. FENNELL.

PROCESS 0F MAKING BIFOCAL LENSES.

FILED Nov.9,1922.

entor- By f s.

Allorneya HARRY FENNELL, OF EVERE'I'T, MASSACHUSETTS.

Pnocn'ss or MAKING BIrocAL LnNsns.

Application med/'November 9, 1922. Serial No. 599,864.

To all whom t mol/y concern:

Be it known. that I, HARRY F'ENNELL, a citizen of the United States,residing at Everett, in` the county of Middlesex' and State ofMaachusetts, have invented certain new and useful Improvements inProcesses of Making B-ifocal Lenses, of which the following is a full,clear, and exact de- -scri tion.

y invention relates to the manufact-ure of bifocal lenses, the sameresiding in av into a recess in a blockof glass of one index ofrefraction a disc of glass of a different indexl of refraction, and alsofusing to said block outside said disc a layer of glass of the sameindex of l refraction as said block. I

It also consists incertain steps, features and details of procedurewhich will be hereinafter more fully described and claimed.

I have illustrated in the accompanyingr drawings the product of each ofthe differ#- ent steps of the'process, as I prefer to carry 1t out. Itis to be understood, however. that my invention is not limited to any ofthe steps or details of the process illustratedand described,'except as1t may be limited by the appended claims. In these drawings Figure 1 isa plan view 4of the block of glass which is to form the body portion ofthe lens or blank;

Figure 2 is a sectional view of the same;

Figure 3 is a sectional view of one form of the composite buttonemployed;

Figure 4 is a similar view of the elements of a lens blank just prior tofusing;

Figures 5 and 6 are similar views of a completed blank, Figure 6 showingin dotted lines where the blank may be ground for the production of afinished lens;

Figure 7 is a sectional view of a `finished uncut lens;

Figure 8 shows the elements of one of the composite buttons after theyhave been united but prior to grinding;

Figure 9 is a sectional view of a modiied' form of button; and

Figure 10 is a similar view of the elements of which the same is made.

In carrying out my process, I form in a block 1 of glass of suitablecontour, a spherical recess or depression 2 and fuse in said recess abutton 3 composed of integral discs or laminae 4 and 5 of glass ofdifferent indices o f refraction. 'Ihe disc or layer 4 should have thesame index of refraction as the glass of the block 1; in practice it ismade from what is commercially known as crown glass. The disc or layer 5is made of glass of a different index of refraction from that of4 thedisc 4 and block 1. It is preferably composed of what is known in thetrade as flint vglass,that is, glass containing lead in its compositionand having a relatively high index of refraction. The Hint glass side ofthe button 3 4has ya convex curvature approximately the same as, butpreferably slightly stronger than, that of the recess 2, as indicated inFigure 4 of the drawing. To fuse the parts together, the but-- ton 3 isplaced in the recess 2, and the two parts of the lens are introducedinto a suitable furnace and subjected to heat, so 'as to cause `thefusion or coalescence of the two parts of the button 3 with the block 1in the recess 2. The fusing operation may be substantially the same asthat no-w followed in the production of the Kryptok bifocal. The productof the fusing operation is the lens blank represented in section inFigure 5 of the drawing. As will be seen, this blank consists of a bodyportion of crown glass, and a reading segment of flint glass enclosedwithin and protected by the body portion'. All the parts are integrallyunited and the crown glass p ortion y4 of the button 3 forms acontinuation of the crown glass body portion. It constitutes a coveringweb or layer of crown glass for the reading segment of flint glass andis preferably relatively thin.

To produce a finished lens from the blank, the usual procedure in theproduction of a lens from a. Kryptok .blank is followed. That is, bothsurfaces are ground to the curvatures desired and the lens cut toeye-size and edged. Care should be exercised, how ever, in the grindingand polishing of the segment side of the lens to remove but a portion ofthe crown glass cover disc 4. In Figure 6, I have illustrated a blankand shown in dotted lines approximately the the amount of the coverlayer 4 which may be removed. Of course, the thickness of this layer-4is not essential, except that it should not be wholly removed at any oneor more points. In other words, at least a film of the crown glass coverlayer 4 should be permitted to remain for the protection of the flintglass reading segment. An uncut finished lens made in accordance with myinvention is illustrated in Figure 7 of the drawing. f

In the production of the composite button 3, shown in Figure 3, I taketwo flat, circular discs 6 and 7 of crown glass and flint glass,respectively, and fuse the same together by a separate preliminary fusinoperation. The disc 46 is preferably a out half the thickness of thedisc7. Convenient thicknesses for the two discs .would be 1% and 3millimeters, respectively. When fused together, as illustrated in Figure8 of the drawing, asegment blank is produced which is afterwards groundconvex and polished upon the flint glass side thereof, as lndicated indotted lines in Figure 8, to form the button illustrated in Figure 3.The convex portion of the button 3 includes the entire exposed surfaceof the flint glass portion 5 thereof and the edge of the crown glassportion 4l When made the proper size, the button, including the crownglass portion thereof, may enter the recess-2 in the crown glass block1, so that during the fusing operation the circumferential edge of thecrown glass portion 4 of the buttonwill become fused to the wall of therecess 2 around the periphery thereof.

Instead of employing a button 3 having the lower side of the crownglassl portion 4 thereof plano, I ma use a button 3, such as isillustratediin igure 9, in which the crown glass ortion 4a is concavedon the side to whic the iii-nt glass portion 5 is joined. In makingsuch' a button I first form aconcave. surface on one side of a` disc 6aof. crown glass and fuse a disc 7a of flint glass to said concavesurface. The segment blank thus formed is afterwards ground convex onthe flint jglass side thereof, as indicated in dotted lines in Figure10, and the button thereby produced may be fused into the recess 2 ofthe block 1 in the manner heretofore de scribed. As the segment side oftheperiscopic lens of Figure 7 'is convex it will be yseen that by theuse of the button' 3a in the production of .such lens there Ais lessdanger ofgrinding away the crown glass layer 4 to such an extent as toexpose a part o r all of the flint glass segment than there is when abutton such as is illustrated in Figure 3 is employed. Y v

While it is essential that the glass of the cover disc 4 be of the4 sameindex of refrac tion as that of the body portion 1, said disc may bemade of colored glass or of glass having' a different dispersive powerfrom that of the body portion. For example, if the cover disc be made ofCrookes or a similar glass, it would give relief to the eyes byfiltering out some of the ultra-violet rays of light that ordinarilywould pass unobstructed through the reading portion of the lens. And ifmade of glass having a different dispersive power from that of the bodyportion, the objection of chromatism present in the Kryptok bifocal maybe overcome.

As the lens and lens blank produced in accordance with my imp rovedprocess forms the subject of a separate application for patent led by meFebruary'23, 1922, Serial No. 538,502, a full detail description of theAadvantages of such a lens is not deemed necessary herein. It issuiiicient to say thaty the lens thus roduced has the reading segment ofsoft int glass wholly protected b the body portion of crown glass, sothat al danger of scratching or abrading the seg.

outside said disc a layer of glassof the same index of refractionl assaid block.

2. The process of making a bifocal lens or blank which comprises' fusinginto a recess in a block of 'crown glass a disc of flint glass and alsofusing a layer of crown glass to said block outside the disc 'of iintglass.

3. The process of making a'bifocal lens blank which consists in fusinginto a recess 1n a block of glass, in a single fusing operation,superposed discs of glass of different indices of refraction.

4. The process of making va bifocal lens blank which consists in fusinginto a recess in a block of glass a button composed of superposedintegral discs or lamin of glass of different indices of refraction.

5. The process of making a lbifocal lens blank which consists in fusinginto a recess in a block of glass discs of glass of different indices ofrefraction, the outer of which is of the same index asthat of saidblock.

6. The process of making a bifocal lens blank which consists in fusinginto a recess in a block .of glass a button composed of integral discsor laminas of glass of different indices of refraction, the outer ofwhich discs is of the same index of refrac tion as said block. f

7. The process `of making a bifocal lens blank which consists in fusinginto a recess in a block of crown glass, superposed discs of Hint andcrown glass.

8. The Iprocess of making a bifocal lens blank which consists in fusinginto a recess in a block of crown glass a button composed of integraldiscs or laminas of Hint' and crown glass.

9. The process of making a bifocal lens vblank which consists in fusinga disc of glass of a certain index of refraction into a recess in ablock of glass of a different index of refraction, and simultaneouslyfusing into the same recess, on top of the first disc, a disc of glassof the same index as said block.

l0. The process of making a bifocal lens blank which consists in fusinga disc of Hint glass into a recess in a block of crown glass andsimultaneously fusing a disc ofvcrown glass into the Same recess, on topof the disc of flint glass.

l1. The process of making a bifocal lens blank which consists in fusingtogether two lmy signature.

pieces of crown and Hint glass, forming a convex surface on the flintglass side of the united pieces, and afterwards fusing the button thusformed into a recess in a block of crown glass.

12. The process of making a bifocal lens blank which consists -in fusingtogether two discs composed respectively of crown and Hint glass,forming a convex Surface on the Hint glass side of the united discs, andafterwards fusing the button thus formed into a recess in a block ofcrown-glass.

13. The process of making a bifocal lens blank which consists in forminga concave surface on one side of a disc of crown glass, fusing a disc ofHint glass to said concave surface, forming a convex surface on the Hintglass side of the united discs and afterwards fusing thebutton thusformed into a recess in a block of crown glass.

In witness whereof, I hereunto subscribe HARRY FENN ELL.

